The article below was written by George Kennedy and
is reprinted from The Abyssinian Breeder magazine

It is apparent that a significant minority
of the subscribers to this magazine does not have a clear understanding of how Abyssinians (and Somalis) inherit coat colour or length. This is evidenced by
the number of impossible and improbable claims made in submissions to the Guide to Breeding Abyssinians - I have to "filter" these to ensure that
other readers are not misled. Again, there is unprecedented
interest in breeding dilute Abys and Somalis, and for me, a frequent need to explain to callers that
what they propose is either downright impossible or else it
has only a tiny chance of succeeding. This article is
therefore provided for the many subscribers who seem to need it. It is devoted to the four
basic, eumelanistic Abyssinian colours and two coat lengths. For
readers on the far side of the Pacific, Tawny = Ruddy and Cinnamon = Red

Some Definitions

Abyssinians
- and indeed all mammals - are what they are because of
their genetic make-up. At conception, a sperm from the
father fuses with an egg from the mother, and the eventual
result is a cat, created because a large number of genes from each parent, as
many as 3000, each carrying a lot of specific information, are combined as a
result of the fusion. Some of the genes determine the number
and shape of paws, other determine the sex, and so on. In this article, I want to talk
about the genes that determine the colour and coat length.

First, it is essential to define a few basic terms.

Phenotype 
this is the
colour/coat length appearance of the cat, e.g.: Cinnamon Aby or Tawny Somali.

Genotype  the genetic make-up
of the cat, for colour and coat length, e.g.: Cinnamon
Somali capable of producing Blues or Blue Aby capable of producing Cinnamons
(must be suitably mated in each case).

Dominant  the dominating or
fallback characteristic, to which cats revert unless
conditions are suitable for something else (come back to
this point - the definitions of this term and the next four
are inter-locking, and it helps to re-read). In this
context, the dominants are Tawny and shorthair. It is thus
quite likely that mating a Cinnamon Somali to a Blue Abyssinian could
result in nothing but Tawny
Abyssinians, but see below.

Homozygous
 not capable of producing any coat colour or length
other than its own (and the dominant of course anyone can produce the dominant), i.e., not "carrying" anything (see below). If you think about
it, you will notice that a homozygous
cat is one whose genotype is the same as the phenotype.

Carrying an Aby/Somali is said to be carrying a colour or coat length when it is capable of
producing offspring of a colour or coat length different
from its own and the dominant. A Tawny Aby could carry
Cinnamon, or a Blue Aby could carry Somali. However, no-one could carry Tawny and no Somali could carry
Abyssinian, because those are the dominants.

Heterozygous the opposite of
homozygous; refers to a cat carrying a colour or coat length.

Recessive
 this is a gene over which the dominant dominates. For instance, mating a homozygous Tawny Aby to a homozygous
Cinnamon Aby will result in all the offspring being Tawny:
Clearly Tawny dominates over Cinnamon. The recessive genes
governing coat colour and length are Cinnamon, Blue and
Somali. Fawn is a combination of Blue and Cinnamon. There is
no partial dominance, so Blue does not dominate over Cinnamon (or vice versa), and neither
of them dominates over Somali (and vice versa). Again, there is no sex linkage, as there
is with certain Tabby colours. This means that males and
females can have all colours and both coat lengths with equal probability.
A most important thing to remember is that kittens of
recessive colour or coat length
are possible only if both parents are capable of producing them. For instance you can
get (some) Somali kittens only if each parent is either a Somali or Somali carrier. This will become clearer as the article
progresses, I hope.

'Well, that was very interesting." I
hear you cry, "but lets get down to tin tacks:
How do I breed Fawn Somalis?!" "With some difficulty," I have to answer,
"and if you dont already know, you might as well
read the rest of this article."

The genotype of a homozygous Tawny
Abyssinian is commonly written AABBDDTaLLThe AA stands for the basic agouti (yellowish-grey) background colour and ticking - it does
not vary from one Aby colour to another. BB
stands for black pigmentation.
It becomes bb(brown) in a Havana or Burmese,
and blbl(light brown)
in the Cinnamon Aby or Somali.

The B,b and bl are associated with
each other, and a series such closely
associated genes are known asalleles The genotype of the Cinnamon Aby is thus the same as for the Tawny, except that BB
is replaced by blbl. For a Tawny carrying Cinnamon, the BBisreplaced by Bbl
in our standard notation.

DD stands for dense
pigmentation, and becomes diluted (and writtendd) in the Blue Aby;
the notation for a Blue carrier is Dd. Fawn is
a combination of Cinnamon and Blue, and hence the genotype of the Fawn Aby is writtenAAblblddTaLL.

Ta is the Abyssinian
tabby coat pattern, being a reduced form of tabby occurring on the face and head but (ideally!)
not on the chest, limbs and tail. It is dominant over the other two tabby alleles: T,the mackerel tabby, and Tb the blotched tabby.

Finally, LL means
that the cat is
shorthaired and homozygous: the genotype of a Somali carrier has Ll and a
Somali has ll. Consequently, the genotype of a Tawny Aby carrying Cinnamon,
Blue and Somali is
AABblDdTaLl.

Breeding Colour Recessives and
Somalis

Cells unite at random during the conception
process. Thus, close to half of all the kittens ever bred are male and half are female,
but there is no rule that says "the last kitten born in this litter was male
therefore the next one will be female". The same applies to the genes governing
colour inheritance. So if a particular mating is equally likely to produce Blues as
Tawnys, you will not get two of each in every litter of four, and it is quite on the cards
that you will get the occasional all-Tawny or all-Blue litter. What it does mean is that.
if such a mating is performed a large number of times (e.g., 20 or more), then on
average half the kittens will be of each colour. It is important to remember that
statistical averages are not prescriptions for individual litters.

An excellent aid to working out what happens when cats of given
genotypes are mated is the "checkerboard" diagram drawn up for that mating, like
the one below showing what happens when a Tawny carrying Cinnamon is mated to another
Tawny carrying Cinnamon. Note that only the variables are shown for simplicity: Clearly,
each cat will have AA, DD, Taand
LL in its genotype.

Genes from Tawny carrying Cinnamon[Bbl]

B bl
Genes from
Tawny carrying B
BB BblCinnamon
[Bbl]
bl Bbl blbl

Each of these intersections is as probable
as any other, and so the checkerboard diagram shows the (statistical average) gene
pairings. You can see that from a mating like this, 25% of the kittens would be homozygous
Tawny (BB), 50% would be Tawny carrying Cinnamon (Bbl)
and 25% would be Cinnamon (blbl). The important conclusions
are that some kittens are Cinnamon, most of the kittens (75%) are Tawny, and most but
not all of the Tawny kittens will carry Cinnamon. Moreover, because Tawny is dominant,
the Cinnamon carriers will look Tawny and you will not be able to tell them apart from
homozygous Tawnys.

Feeling brave? If you are, lets try
to see what can happen when a Tawny Aby carrying Blue and Somali is mated to a Tawny
Somali carrying Blue.

, but the chances (1 in 8) are not great.
Incidentally, you should be able to tell by inspection that
if both cats had been Tawny Abys carrying Blue and Somali,
the chances of breeding a Blue Somali would have been only 1
in 16.

Once more with feeling: What do you get
when you mate a Cinnamon Aby carrying Blue to a Blue Aby carrying Cinnamon?

This mating, on average, produces 1/4
BblDd
(Tawny carrying Cinnamon and Blue), ¼ Bbldd (Blue carrying
Cinnamon), ¼ blblDd (Cinnamon carrying Blue), and ¼
blbldd
("Blue and Cinnamon", i.e., Fawn). This mating represents one of the two best
chances of getting a rainbow litter, but dont expect one the first time you try! The
other mating giving exactly the same result (on average) is Tawny carrying both to Fawn.

and Fawn;
this results in 45 different combinations (not 9² = 81 because there are
duplications). Dealing with each in detail would fill the magazine. Moreover, if Somalis
are added, we get 27 genotypes (the 9 above, plus the same 9 carrying Somali, plus the
same 9 being Somali) and the total number of combinations becomes 378. Just the same, I
once worked out what you get when mating two Tawny Abys carrying Cinnamon, Blue and
Somali. It took an 8 X 8 checkerboard, and as expected, you get (on average) all 27
varieties, including a 1 in 64 chance of breeding a Fawn Somali. The table below is a
reprint from an earlier article of mine and gives the results in a nutshell.

If you want to know what to expect from a
litter involving Somalis or Somali carriers that are or carry Cinnamon or Blue, just
substitute Somali for the missing colour in the Average
Litter Expectations table. So, if you happen to be interested in Somalis and Blues,
substitute Somali for Cinnamon in the table, and just
remember that where blbldd gave a Fawn Aby, the
ddll
combination represents the Blue Somali. A table including Cinnamon, Blue and Somali is too
large for inclusion, but most of the results can be extrapolated from the table provided.

Does My Cat Carry XYZ?

No, if it is already

XYZ
-
thus a Blue Aby does not carry Blue (neither does a
Fawn carry Cinnamon or Blue. because it represents a combination of both). No,
if XYZ
is Tawny or shorthair, because those
are dominants and all Abys/Somalis can produce them if suitably mated. No, if
neither parent is or carries
XYZ, except for one-in-a-million mutations like the Scottish
Fold or Cornish Rex. Yes, has one
XYZ
parent. Yes, if It has produced
at least one
XYZ
kitten. Maybe, if neither parent is
XYZ
but one or
both parents carry
XYZ.

If the answer is "maybe", you can find the chances of that
"maybe" by looking up the preceding table. For example, if both your cats
parents are Tawny carrying Cinnamon, your cats chances of being a Cinnamon carrier
are 2 out of 3 (think about it: 25% of offspring on average are Cinnamon while 75% are
Tawny; 50% carry Cinnamon, so your cats chances are 50/75 = 2/3). On the other hand,
if you mate a Tawny carrying Blue to one carrying both Blue and Cinnamon, and your kitten
is Blue, its chances of being a Cinnamon carrier are 1/2 (12½ divided by 12½ + 12½).
However, cats that carry do not normally look different from cats that dont, and
thus the only way to be sure is to prove it by getting your cat to produce

XYZ
kittens.

Proving That a Cat Carries (or Does
Not Carry)

XYZ

There are really two aspects to this
question:

What is the best way of working out whether a cat carries

XYZ
(i.e., Cinnamon, Blue,
Somali or any combination thereof)?

When do you give up and decide that the cat does not carry

XYZ, after all?

The first one is easy. Test mate your cat to an "XYZ cat",
i.e., to a Cinnamon (or Fawn) when testing for Cinnamon, to a Blue (or Fawn) when testing
for Blue, to a Somali when testing for Somali. Wherever you look in the earlier table, you
can see that you have twice the chance of breeding XYZ when one of the cats is XYZ
and the
other is a carrier than if both are carriers. The other important thing is that if you are
testing for a lot of things, you should test one after the other; that is really
faster than trying to test for everything at once, unless you get lucky. Thus, if you hope
your Tawny cat may carry Blue and Cinnamon, it will be faster to prove that if you mate it
to a Cinnamon and next time to a Blue, than to a Tawny carrying both. Those of you who
catch on fast (i.e., the vast majority of subscribers), will have already worked out that
the best sort of "test cat" is a Fawn Somali.

Let us now look at the second question. You've mated your Tawny female
which you hope carries Cinnamon to a Tawny that definitely carries Cinnamon (you had no
access to a Cinnamon stud), and all four kittens in the litter are Tawny. On average, a
quarter of them should be Cinnamon - does that mean that your cat doesnt carry? As
it happens, the answer is no - your cat could still carry, and indeed the chances of there
being no Cinnamon kittens in a quartet from such a mating are nearly 32%. That is, your
cat still has a 32% chance of being a carrier.

The laws governing this sort of thing are the laws of chance - laws
that could answer a question like "what are the chances of getting tails seven times
in a row when fairly tossing an unbiased coin"? Accordingly, the formulae tend to be
complicated, and all I propose to do here is to give you a table that covers most of the
eventualities. The table is drawn up for Tawny carrying X (Tx) mated to X or Tx. but it
would work in exactly the same way for (say) a Cinnamon carrying Blue, or a Blue carrying
Somali.

Rather interesting, isnt it? For example, you can now work out
how "odds-defying" some of your litters have been. More importantly, you can
calculate your cats chances of being a carrier of "X", where X is of
course equally applicable to Cinnamon, Blue or Somali. Statistically, an event can be discounted if its probability falls below 1%.
Thus, even getting no Blue kittens in a litter of 6 in a Blue X "maybe Blue
carrier" mating, does not quite put paid to a cats chances of being a carrier.
However, a second - even small - litter without Blues to a Blue would mean you should give
up on this cat.